Unable to generate proper certificate on 8.0 Open Source edition

Basically I been trying to avoid those Zimbra Collaboration Server messages shown in certificate. Been following all available guides in wiki, but info there looks outdated, at first I saw that /opt/zimbra/ssl/zimbra/ca/zmssl.cnf is being overwritten when making certificate (not CA) for some reason. Then I managed to bypass that, but still, when CRT is generated and deployed to server, the new certificate with completely different contents inside is being shown to public. Can anyone provide me correct instructions or manual or anything else which could help me make absolutely custom certificate ?